1. Field of the Invention
The invention relates to the field of calibration of analog circuits and, in particular, relates to the calibration of the gain of multiple channel amplifiers wherein temperature compensation and automatic gain control is provided to each channel.
2. Description of Related Art
In certain types of applications, automatic gain control of an amplifier is essential to the effective or useful functioning of the system. Such applications include radar systems, and communication systems, and particularly those radar systems which include multiple amplifier channels where the gain of the multiple channels must be equalized. Clearly, in systems like radar systems in which precise instrumented electronic measurements are continually being made as an essential part of the systems' functioning, any drift in gain in even one of the multiple channels will destroy the absolute accuracy of measurement which is attempting to be made.
In the prior art, gain adjustments in amplifiers in radar systems were made using a delta automatic gain control circuit (AGC) for multiple channels of the amplifier. However, even where each channel is separately compensated, the relative gain among channels must not only be initially calibrated or equalized, but such equalization must be maintained over time as well. Therefore, the prior practice has been to provide an additional delta AGC circuit to compensate for drifts in gain among the various channels of a multiple channel amplifier. Nevertheless, such prior art designs require periodic calibration to match the gain of the multiple channels. This calibration must be achieved through the use of sophisticated, delicate and high precision built-in test equipment.
What is needed, then, is a simple procedure for calibrating an amplifier and a design for an amplifier which includes an automatic gain control which is of such a nature that calibration can be made in the field without the need of sophisticated built-in test equipment.